Dispatch host mainExecutor callbacks through the main looper

tools/chatgui-android/router-tests/src/main/kotlin/android/content/Context.kt

@@ -22,6 +22,7 @@ open class Context {
         const val RECEIVER_NOT_EXPORTED = 4
     }
     val packageName = "com.utun.chat"
+    val mainExecutor = java.util.concurrent.Executor { task -> android.os.Handler(android.os.Looper.getMainLooper()).post(task) }
     var cacheDir = File(System.getProperty("java.io.tmpdir"), "utun-router-host-cache")
     val contentResolver = ContentResolver()
     var vibrator: Vibrator? = Vibrator()